Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/0081—Composite particulate pigments or fillers, i.e. containing at least two solid phases, except those consisting of coated particles of one compound
  • C09C1/0084—Composite particulate pigments or fillers, i.e. containing at least two solid phases, except those consisting of coated particles of one compound containing titanium dioxide
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values

Definitions

• the present invention relates in general to the treatment of titanium bearing materials to form hydrated or dehydrated titanium oxides, and in particular to a process for preparing a composite titanium dioxide hydrate which may be calcined directly to pigment material having the structure of rutile.
• titanium dioxide pigments for .commercial use at the .present time depend almost exclusively upon the reaction of titaniferous bearing materials, and in particular ilmenite, with sulfuric acid.
• ilmenite is a mineral which, in general, may be referred to as an iron titanate (FeTiO and is composed principally of titanium oxide and iron fractions in the form of ferric oxide and ferrous oxide.
• the admixture in general, in the treatment of ilmenite with concentrated sulfuric acid, the admixture is heated until a reaction between the ilmenite and acid sets in. The digestion cake which results from this reaction is then dissolved in water and the ferric iron values reduced to ferrous iron by adding metallic iron to the solution. Thereafter the solution is clarified and a so-called extender, such as, for example, calcium sulfate, is added and the mixture boiled (hydrolyzed) until substantially all of the titanium is precipitated out as a composite hydrolysate having the form of an anatase titanium dioxide modification which is subsequently filtered, washed and calcined to produce a composite pigment material.
• a so-called extender such as, for example, calcium sulfate
• Modifications of this procedure include the addition of an-cxtender in the form of an aqueous slurry to a precipitated titanium dioxide hydrate; or mixing the aqueous extender into a titanium sulfate solution prior to hydrolysis.
• the calcined hydrolysate has remained substantially in the form of anatase, and hence it has been necessary to treat the hydrolysate, before calcination, with a suitable promoter so as to cause the anatase modification to convert to the rutile modification whereby the calcined pigment will possess the characteristic whiteness of color, fine particle size, soft texture, improved tinting strength, and other Well-known characteristics of rutile.
• An object of the present invention is to provide an improved'method of producing a composite titanium dioxide pigment of rutile structure.
• a further object of the invention is to provide a method for precipitating a titanium hydrate upon an extender to form a composite titanium dioxide hydrate which, when calcined within a temperature range suitable for optimum pigmentary particlesize and without the addition of a promoter, will form a composite rutile pigment.
• a further object of the invention is to provide a sulfate solution prepared from a hydrochloric acid leached ore residue for use in the preparation of composite pigments from which may be precipitated an anatase titanium dioxide modification which is easily convertible ,to the rutile structure by calcination.
• a still further object of the invention is to provide an improved method for forming an anatase titanium dioxide modification easily convertible to rutile without the use of a promoter wherein a hydrochloric acid leached ore residue is used in preparing the sulfate solution from which the hydrateis precipitated.
• the present invention relates to the discovery of an improved method for making a composite pigment of rutile structure by mixing an extender with a titanium sulfate solution prepared by the use of a hydrochloric acid leached ore residue, precipitating a composite hydrate from the solution and thereafter calcining the washed and dried composite hydrate directly to form a composite titanium dioxidev pigment of rutile structure.
• a sulfate solution may be prepared from the digest of a hydrochloric acid leached residue alone, it is within the purview of the invention to form a sulfate solution from the digest of a mixture of a titaniferous material as, for example, a titaniferous ore, ore concentrate or titaniferous slag, and a hydrochloric acid leached ore residue; or by the admixture of separate sulfate solutions formed from a titaniferous material and a hydrochloric acid leached ore residue respectively.
• a titaniferous material as, for example, a titaniferous ore, ore concentrate or titaniferous slag, and a hydrochloric acid leached ore residue
• leached ore sulfate solution shall be understood to mean a titanium sulfate solution which has been prepared by the use of a hydrochloric acid leached ore residue alone or prepared by admixtures of the latter with ores orslags in the manners suggested above.
• composite as used in conjunction with the hydrate and calcined pigment, shall be understood to connote the use, at hydrolysis, of an extender, such as, for example, bariunr or calcium sulfate, upon which the titanium dioxide hydrate is deposited as a coalesced precipitate.
• an extender such as, for example, bariunr or calcium sulfate
• calcium sulfate anhydrite, barium sulfate or strontium sulfate may be used as extenders, it has been found that calcium sulfate anhydrite is highly satisfactory from a commercial standpoint, and hence the extender referred to in describing and illustrating the present invention will be a calcium sulfate anhydrite, the composite pigment formed from the coprecipitated hydrate being sometimes termed a calcium base pigment.
• the hydrochloric acid leached ore residue referred to herein is a fine titanium dioxide rutile modification, comprising substantially TiO precipitated from a titanium-iron-chloride solution obtained by leaching a titaniferous ore with hydrochloric acid at elevated temperatures to remove the bulk of the iron.
• a titaniferous ore ground to a particle size of about 0.5 to 2.0% plus 200 mesh is mixed with concentrated (20 Be.) hydrochloric acid in the ratio of about 1 part ore to 2.25 parts HCl (20 B.) and heated to a temperature of about C.
• the titanium sulfate solution may be prepared from an acid leached ore residue alone by digesting the latter in concentrated sulfuric acid.
• the digestion treatment comprises mixing the acid leached ore residue with concentrated (96%) sulfuric acid in an amount such that the ratio of acid, calculated as 100% H SO to acid leached ore residue is within the range of 1.7 to 1.8 parts acid to 1 part acid leached ore residue, heating the mixture for from A to /2 hour at a temperature of from 80 to 120 C. and thereafter adjusting the acid concentration for reaction to from about 86% to 88% and continuing the reaction until a digestion cake sets up.
• the digestion cake is then cut with water and the solution filtered to form a clarified leached ore sulfate solution having a titanium dioxide concentration of from 180 to 210 grams per liter.
• the hydrolysis of a sulfate solution for precipitating a composite hydrate is accomplished by introducing into the sulfate solution, prior to hydrolysis,.an extender, such as, for example, a slurry of calcium sulfate anhydrite (CaSO prepared as described in U. S. Patent No. 1,906,730, Washburn, May 2, 1933, and the U. S. patents referred to therein.
• a calcium sulfate slurry may be used to advantage as an extender in the manufacture of a composite titanium pigment, it will be understood that other extenders may be used as, for example, blanc fixe, natural silica, etc.
• Hydrolysis of the leached ore sulfate solution is carried out by mixing the leached ore sulfate solution with the calcium sulfate, preferably as an aqueous slurry of about solids and in the ratio of about 2.0 to 2.4 CaSO to TiO maintained at nearly the boiling point for about 4 hours until a major portion of the composite hydrate has been precipitated.
• the composite hydrate which is a titanium dioxide anatase modification is then filtered or otherwise separated from the mother liquor and Washed with a suitable acid to remove excess alkali and sulfates.
• Rutilization of the washed composite hydrate is effected directly, that is to say without the use of a rutile promoter, and is carried out under relatively conventional conditions, the calcination temperatures ranging from 900 C. to 975 C. and the time of calcination ranging from 3 to 9 hours, the temperatures of calcination being increased in increments of about 25 C. for periods of time of decreasing length during calcination.
• a calcined composite titanium dioxide pigment material obtained by the process of this invention exhibits high tinting strength, clear White color, soft texture and 80% to 90% of the pigment in the form of rutile.
• the sulfate solution to which the extender is added to form a composite titanium dioxide hydrate may be formed from the digest of a hydrochloric leached ore residue alone, in the manner described above, or from the digest of a mixture of a titaniferous material, such as a titaniferous ore, or concentrate, or titaniferous slag, and a hydrochloric acid leached ore residue.
• the digest of a mixture of a titaniferous ore such as, for example, the ore produced at the Mac- Intyre Mines at Tahawus, New York, commonly known as MacIntyre ore
• a leached ore residue is carried out by mixing ground MacIntyre ore with concentrated sulfuric acid and a hydrochloric acid leached ore residue in suitable proportions which experiments have shown are critical for the production of a leached ore sulfate solution which, upon admixture with an extender, may be hydrolyzed to form a coalesced precipitate having high convertibility to rutile upon calcination.
• Typical of a MacIntyre ore which may be used in the digest is one which analyzes as comprising about 45% TiO about 34% total iron and the remainder gangue, and which has been ground preferably to a particle size of from 0.5 to 20% plus 200 mesh.
• the hydrochloric acid leached ore residue prepared in the manner already described is preferably added to the MacIntyre ore as a dehydrated, relatively coarse, sand-like material, the amount of acid leached residue being at least about 4% and preferably not less than about 5% on a TiO basis.
• the percent rutilization of the calcined composite pigment will be from to It has been observed that, in general, the tinting strength values of a calcium base pigment formed from a leached residue sulfate solution prepared from these source materials increases with an increase in acid concentration at digestion, and especially high tinting strength values have been obtainedwith acid concentrations at digestion in the range of from 86 to 88%.
• the ratio of sulfuric acid to ore and ore residue at digestion being from about 1.50 to 1.80, based on the total amount of admixed ore and acid leached ore residue, within which range a leached ore sulfate solution is formed from which coalesced precipitates are obtained having high conversions to rutile.
• the total amount of concentrated sulfuric acid required for digestion is placed in a digestion pot with the admixed titanium source materials, i. e. the MacIntyre ore and acid leached ore residue in ratios Within the range described above, and the mixture heated to a temperature from C. to C., whereupon cold water is added to adjust the acid strength to a concentration ofabout 88% at reaction. Heating is continued until a digestion cake is for-med and sets up, whereupon the cake is removed from the digestion pot and dissolved in water.
• the admixed titanium source materials i. e. the MacIntyre ore and acid leached ore residue in ratios Within the range described above
• the mixture heated to a temperature from C. to C., whereupon cold water is added to adjust the acid strength to a concentration ofabout 88% at reaction. Heating is continued until a digestion cake is for-med and sets up, whereupon the cake is removed from the digestion pot and dissolved in water.
• the ferric iron values of the aqueous solution are reduced to the ferrous state by adding scrap iron or the like thereto and thereafter the solution is filtered and clarified to provide a leached ore sulfate solution having a titanium dioxide concentration of from to 210 grams per liter.
• an extender such as, for example, calcium sulfate anhydrite
• an extender is introduced into the leached ore sulfate solution, preferably in the form of an aqueous slurry of 30% solids prior to hydrolysis and in the ratio of about 2 parts CaSO, to 1 part TiO Hydrolysis of the composite leached ore sulfate solution is carried out by heating the admixture and maintaining it at the boiling point until a coalesced composite hydrate has been precipitated.
• the precipitate is then filtered or otherwise separated from the mother liquor and washed preferably with a suitable acid to remove the ferrous sulfate.
• Rutilization that is to say conversion of the composite titanium dioxide precipitate to rutile, is accomplished directly by calcination, that is to say without the use of a rutile promoter before calcination, and is carried out under substantially the same conditions used for calcining promoted hydrates, the calcination temperatures ranging from 900 to 975 C. and the time of calcination ranging from 3 to 4 hours, the temperature of calcination being increased periodically during calcination.
• a calcined pigment prepared in the above described manner will comprise from 80 to 100% TiO in the form of rutile.
• the instant invention embodies the concept and method of forming a sulfate solution from a mixture of a titaniferous slag and a hydrochloric acid leached ore residue.
• the titaniferous slag used may be obtained by smelting titaniferous iron ores in the presence of a carbonaceous reducing agent to produce a slag which has a low iron fraction but which is rich in titanium values.
• a typical slag is one formed from ilmenite ore and analyzing as high as 67% TiO and 5% total iron.
• the slag is ground preferably to a particle size in the range of from 0.5 to 2.0% plus 200 mesh.
• the titanium sulfate solution is prepared from a mixture of the ground slag and the hydrochloric acid leached ore residue.
• the ratio of slag to acid leached ore should be about 4 to 1 on a TiO basis, but it will be understood that some variation in this preferred ratio may be made with satisfactory results.
• concentrated sulfuric acid in a ratio within the range of from about 1.6 to 1.7 parts acid to 1 part of the ore-slag admixture, and the mixture heated to about 120 C. within a period of from to 45 minutes, whereupon the acid concentration is adjusted for reaction to about 88%, the reaction being continued until a digestion cake sets up.
• the digestion cake is then cut with water and the solution filtered to form a clarified leached ore sulfate solution having a titanium dioxide concentration of from 180 to 210 grams per liter.
• the hydrolysis of the leached ore sulfate solution formed from the digest of a slag and an acid leached ore residue is accomplished by introducing into the sulfate solution or otherwise admixing therewith, preferably prior to hydrolysis, an extender, such as a slurry of calcium sulfate anhydrite of about 30% solids and in the ratio of about 2 parts CaSO to 1 part TiO and then heating the mixture and maintaining it at nearly the boiling point for about 4 hours until a large portion of the composite hydrate is precipitated.
• the composite hydrate which is a titanium dioxide anatase modification, is then filtered or otherwise separated from the mother liquor and washed with a suitable acid to remove excess alkali and sulfates.
• Rutilization of the washed composite hydrate is effected directly, that is to say without the use of a rutile promoter before calcination, and is carried out under relatively convention conditions used for calcining promoted hydrates, the calcination temperature ranging from 900 to 975 C. and the time of calcination ranging from 3 to 4 hours, the temperatures of calcination being in-' creased periodically during calcination.
• a calcined composite titanium dioxide pigment obtained from the digest of an admixture of a titaniferous slag and a hydrochloric acid leached ore relsidue exhibform of rutile.
• ADMIXED SULFATE SOLUTIONS A still further modification of the procedures described above for forming composite pigments, by the use of hydrochloric acid leached ore residues is that of admixing a sulfate solution prepared from a hydrochloricacid leached ore residue, as in the manner described above, with a sulfate solution prepared from-a titaniferous ore or from a titaniferous slag.
• Example I To 1000 parts Maclntyre ore prepared in the manner hereinabove described and having a particle size of 0.9% plus 200 mesh was added 1700 parts 96% sulfuric acid, the ratio of acid, calculated as 100% sulfuric acid, to ore being 1.77. The mixture was heated initially to a temperature in the range of from 110 C. to 120 C., whereupon cold water was added to adjust the acid concentration at reaction to 88%. Heating was continued for about /2 hour at the end of which time the digestion cake had formed and set up.
• the clarified sulfate solution was then admixed with a calcium sulfate slurry containing about 30% solids in the ratio of about 2.3 CaSO to TiO the acidity of the solution being adjusted to about 16.6% by the addition of sulfuric acid.
• Example 11 From the foregoing example it is manifest that upon calcining a calcium base pigment prepared from Mac- Intyre ore alone, i. e. without-the use of a rutile promoter, substantially none of the Ti component is converted to rutile while calcination of a calcium base pigment prepared from hydrochloricacid leached ore residue alone effects substantially 100% conversion of the TiO componentto rutile. i
• a second mixture of the Maclntyre ore and leached ore residue sulfate solution was made but in this instance in the ratio of 90% MacIntyre ore solution to 10% leached ore residue solution on a TiO basis.
• substantially 60% of the TiO component was converted to the rutile structure, the tinting strength of the composite calcined pigment being about 560.
• Example 111 To further illustrate the invention, a titaniferous ore and hydrochloric acid leached ore residue were mixed together prior to digestion to form a leached ore sulfate solution for the production ofa composite pigment convertible to the rutile modification by calcination alone.
• the digestion cake was then dissolved in water and the ferric iron values reduced to ferrous iron by the addition of scrap iron or the like.
• the solution was then filtered and clarified to produce a leached ore sulfate solution which analyzed as follows:
• the solution was boiled for four hours, whereupon about 94.7% of the TiO was precipitated out as a composite hydrolysate. The latter was separated from the liquor, washed, and then calcined for one hour at about 925 C. and for one hour at about 950 C. The calcined. calcium base pigment analyzed as comprising substantially rutile. The tinting strength of the pigment was about 597.
• a second digest was made from a mixture of the Mac: Iutyre ore and the hydrochloric acid leached ore residue in which the ratio of ore to leached ore residue on a TiO basis was about 8.9.
• the treatment of the admixture to form a digest cake from which a leached ore sulfate solution and ultimately a composite hydrolysate was produced was substantially as described above. In this case substantially 80% of the calcined pigment was converted to rutile, the tinting strength of which was as high as about 613.
• Example IV As an example of the use of a mixture of a titaniferous slag and hydrochloric acid leached ore residue prior to digestion to produce a composite pigment convertible to the rutile modification by calcination alone, i. e. without the use of a rutile promoter, a slag analyzed as comprising about 66.8% TiO and 5% iron and having a particle size of 0.5% plus 200 mesh was mixed with a hydrochloric acid leached ore residue of the specifications described above in the ratio of 4.2 parts slag to leached ore residue on a TiO basis. To the admixture was added 96% sulfuric acid, the ratio of acid, calculated as 100% H 30 to the total ore mixture being 1.695. The mixture was heated initially to from about to C, whereupon,
• the clarified leached ore sulfate solution was then admixed with a calcium sulfate slurry containing about 31.5% solids in the ratio of 2.36 parts CaSO to TiO
• the acidity of the solution was adjusted to about 18% at hydrolysis by the addition of sulfuric acid.
• the admixture had the following analysis:
• the solution was boiled for about four hours, whereupon about 96.5% of the TiO was precipitated out as a composite hydrolysate.
• the latter was separated from the liquor, washed and then calcined for two hours at 950 C., at the end of which time 90% of the calcium base pigment was converted to rutile, the tinting strength of the component pigment being about 610.
• Example V The effect of a hydrochloric acid leached ore residue in converting composite hydrolysates directly to rutile calcined pigments is also illustrated by the instant example wherein a sulfate solution is prepared from a mixture of the sulfate solutions formed from the digests of a titaniferous slag and a hydrochloric acid leached ore residue respectively.
• the slag solution was formed by digesting a slag in concentrated (96%) sulfuric acid in the ratio of 1.65 parts acid, calculated as 100% sulfuric acid, to slag, the percent acid concentration at reaction being adjusted to 88%.
• the digestion cake was dissolved in water and the ferric iron values reduced to ferrous iron by the addition of scrap iron.
• the solution was filtered and clarified to produce sulfate solutions which analyzed as follows:
• a sulfate solution was also formed from a hydrochloric acid leached ore residue by digesting the leached ore residue in the manner hereinabove described to produce The'two solutions were then mixed in the ratio of 4 parts slag solution to 1 part leached ore solution, the admixture having the following analysis:
• the solution was boiled for 4 hours whereupon about 96.8% of the Ti0 was precipitated as a composite hydrolysate.
• the latter was separated from the liquor, washed and then'calcined for two hours at 950 C. and for two hours at 975 C., at the end of which time substantially of the composite pigment was converted to rutile, the tinting strength of the composite pigment being from 610 to 620.
• Example VI By way of comparison, a sulfate solution was prepared from a slag solution alone having the analysis given in Example V above. To this solution was added a calcium sulfate slurry of about 30.2% solids in the ratio of 2.36 CaSO to TiO After adjusting the acidity of the solu tion, it analyzed as follows:
• a process for the manufacture of a composite pigment material comprising titanium dioxide in rutile form and an extender which includes: heating a mixture of titaniferous ore and hydrochloric acid in the ratio of about 112.25 to precipitate a substantially iron-free hydro chloric acid leached ore residue digesting said hydrochloric acid leached ore residue in the presence of concentrated sulfuric acid the ratio of acid to leached ore residue being in the range of from 1.5 to 1.8 to form a digestion cake; solubilizing said digestion cake in water to form an aqueous leached ore sulfate solution; mixing.
• a process for the manufacture of a composite pigment material comprising titanium dioxide in rutile form and an extender which includes: heating a mixture of titaniferous ore and hydrochloric acid in the ratio of about 1:2.25 to precipitate a substantially iron-free hydrochloric acid leached ore residue digesting a mixture of titaniferous ore and said acid leached ore residue in the presence of concentrated sulfuric acid to form a digestion cake, said acid leached ore residue being present in said admixture in an amount within the range of from 4% to 20% on a titanium dioxide basis and the ratio of sulfuric acid to the admixed ore and acid leached orc residue being in the range of from 1.6 to 1.8; solubilizing said digestion cake in water to form an aqueous leached ore sulfate solution; mixing an extender selected from the group consisting of the sulfates of barium, calcium and strontium with said leached ore sulfate solution; hydrolyzing said admixture
• a process for the manufacture of a composite pigment material comprising titanium dioxide in rutile form and a calcium sulfate extender which includes: heating a mixture of titaniferous ore and hydrochloric acid in the ratio of about 1:2.25 to precipitate a substantially iron-free hydrochloric acid leached ore residue mixing 'a titaniferous ore with said hydrochloric acid leached ore residue with the acid leached ore residue being present in said mixture in an amount within the range of 5% to on a titanium dioxide basis; digesting the admixed ore and acid leached ore residue in the presence of concentrated sulfuric acid to form a digestion cake, the ratio of sulfuric acid to the admixed ore and acid leached ore residue being about 1.7; solubilizing said digestion cake to form a leached ore sulfate solution; mixing a calcium sulfate slurry of about 30% solids content with said leached ore sulfate solution; hydrolyzing said
• a process for the manufacture of a composite pigment material comprising titanium dioxide in rutile form and an extender which includes: heating a mixture of titaniferous ore and hydrochloric acid in the ratio of about 1:2.25 to precipitate a substantially iron-free hydrochloric acid leached ore residue mixing a titaniferous slag with said acid leached ore residue with the acid leached ore residue being present in the admixture in an amount of about on a titanium dioxide basis; digesting the admixed slag and acid leached ore residue in concentrated sulfuric acid to form a digestion cake, the ratio of sulfuric acid to the admixed slag and leached ore residue being in the range of 1.6 to 1.8; solubilizing said ratio of about 1:2.25 to precipitate a substantially ironfree hydrochloric acid leached ore residue mixing a titaniferous slag with said acidleached ore residue with.
• a process for the manufacture of a composite pig ment material comprising titanium dioxide in rutile form and an extender which includes: heating a mixture of titaniferous ore and hydrochloric acid in the'ratio of about 1:2.25 to precipitate a substantially iron-free hydrochloric acid leached ore residue digesting a titaniferous material in sulfuric acid to form a sulfate solution the ratio of acid to said titaniferous material being about 1.65; digesting said hydrochloric acid leached ore residue in concentrated sulfuric acid the ratio of acid to leached ore residue being in the range of from 1.5 to 1.8 to form a second sulfate solution; admixing the sulfate solutions formed from the titaniferous material and the hydrochloric acid leached ore residue respectively with the latter solution being present in the admixture in an amount within the range of from 4% to 20% on a TiO basis; mixing an extender selected from the group consisting of the sulfates of barium, calcium
• a process for the manufacture of a composite pigment material comprising titanium dioxide in rutile form and an extender which includes: heating a mixture of titaniferous ore and hydrochloric acid in the ratio of about 1:2.25 to precipitate a substantially iron-free hydrochloric acid leached ore residue digesting a titaniferous slag in sulfuric acid to form a sulfate solution, the ratio of said acid to said slag being about 1.65; digesting said hydrochloric acid leached ore residue in concentrated sulfuric acid, the ratio of said acid to leached ore residue being in the range of from 1.5 to 1.8 to form a second sulfate solution; admixing the sulfate solutions formed from the titaniferous slag and the hydrochloric acid leached ore residue respectively, the latter being present in an amount from 5% to 10% on a Ti0 basis; mixing an extender selected from the group consisting of the sulfates of barium, calcium and strontium with said admixe
• a process for the manufacture of a composite pigment material comprising titanium dioxide in rutile form and calcium sulfate anhydrite which includes: heating a mixture of titaniferous ore and hydrochloric acid in the ratio of about 1:2.25 to precipitate a substantially ironfre'e hydrochloric acid leached ore residue digesting a titaniferous material in the sulfuric acid to form a sulfate solution, the ratio of acid to the titaniferous material being about 1.65; digesting said hydrochloric acid leached ore residue in concentrated sulfuric acid to form a second sulfate solution, the ratio of sulfuric acid to hydrochloric acid leached ore residue being about 1.60; mixing the sulfate solution formed from the titaniferous material with the sulfate solution formed from the acid leached ore, residue with the latter solution being present in the 13 I4 admixture in an amount to within the range of from 5% References Cited in the file of this patent to 10% on

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